In order to record data on a disk, means for performing guidance for forming data tracks becomes necessary. For this reason, it has been practiced that grooves are formed in advance as pregrooves, and the grooves or lands (parts whose cross sections are shaped as a plateau, sandwiched between grooves) are used as data tracks.
Also, there is a need to record address information so that data can be recorded at a predetermined position on the data tracks. This address information is recorded by causing grooves to wobble (meander) or by forming prepits on the data tracks.
For example, among DVDs (Digital Versatile Discs), in DVD-RWs, which are rewritable disks using a phase change recording method, and DVD-Rs, which are recordable disks using an organic pigment change method, as shown in FIG. 4, wobbling grooves G are formed as preformats on the disk, and also, land prepits LPP are formed in the lands L portions between the grooves G and G.
In this case, reflected light information obtained by the wobbling grooves is used for controlling the rotation of the disk and generating a recording master lock. Furthermore, land prepits are used to determine accurate recording positions in bit units and to obtain various kinds of information of the disk, such as preaddresses. That is, the addresses indicating the physical position on the disk are recorded as land prepits LPP.
In a disk drive device compatible with such a disk, by reading an address recorded as land prepits LPP on the disk during playback or recording, the position on the disk during recording or playback is confirmed, and various kinds of control are performed.
However, after information is recorded in the grooves, which are recording tracks, the land prepits LPP become difficult to read as a result of interference by pits (phase change pits, etc.) formed in the grooves. Furthermore, the land prepits LPP of the disk after information is recorded become difficult to read depending on the status of an optical pickup (recording/playback head), for example, variation of the position of the photodetector for detecting reflected light, and various kinds of aberrations.
FIGS. 5A to 5C show a read waveform corresponding to land prepits LPP. FIG. 6 shows data recorded by land prepits LPP.
The land prepits LPP, as shown in FIG. 4, are formed by cutouts in the lands in synchronization with the wobble, and three land prepits LPP represent one bit of the address data. That is, as in FIG. 6, if b2, b1, and b0 as (the presence or absence of) the three land prepits LPP are “1, 0, 1”, this is assumed to represent “1”, and if “1, 0, 0”, this is assumed to represent “0”.
The information of such land prepits LPP can be obtained as reflected light information from the disk in accordance with a so-called push-pull signal. That is, this information is difference information of the amounts of reflected light on the right and left with respect to the direction of the track lines.
In this push-pull signal, as shown in FIG. 5A, a comparatively large amplitude is obtained in such a manner as to correspond to the land prepits LPP, and by detecting this amplitude, the information of the land prepits LPP can be detected. For example, the binarization of that information using, for example, a predetermined threshold level makes it possible to detect “1” or “0” as b2, b1, and b0 of the land prepits LPP.
Here, in the case of a state in which data is not recorded on the groove tracks, the amplitude waveform formed by the land prepits LPP becomes a sharp waveform, as shown in FIG. 5B in such a manner as to be expanded in the direction of the time axis, that is, a waveform in which the eye is open satisfactorily. Therefore, the land prepits LPP information can be extracted properly.
However, when data is recorded in the groove tracks, as shown in FIG. 5C, the eye pattern waveform blurs, and the detection of “1” or “0” as b2, b1, and b0 of the land prepits LPP becomes difficult. As a result, the address error rate is deteriorated.
The fact that, after the data is recorded, the address reading by the land prepits LPP becomes difficult in this manner means that, for example, when additional recording is performed on a disk after recording or when a seek is performed, the address cannot be obtained satisfactorily, and the operation performance decreases.
In order to avoid this situation, incorporation of a pickup in good condition with high accuracy has been considered. In that case, selection of the pickup to be incorporated and use of an expensive pickup with high accuracy become necessary, resulting in an undesirable cost increase of the disk drive device.